Regarding speedsters in Marvel Comics, their powers haven’t been developed out as much as those of the Speed Force in DC. Each speedster appears to derive their strength from something or somewhere different, and Marvel seldom addresses the issue over who is the quickest.
Even with the debut of Blur, Marvel’s equivalent of The Flash, the company has never given any thought to who is genuinely the quickest in their universe. That question, however, has been answered with only one panel in a new comic. And it is not at all who everyone expects it to be.
In Avengers #50 (via CBR), Deathlok lets Robbie Reyes, the current Ghost Rider, know that his Hellcharger, his car powered by the Spirit of Vengeance, can outrun anything in the known universe if fully unleashed. This would make the Ghost Rider, by extension, the fastest character in all of Marvel.